Protein prenylation is the attachment of 15-carbon farnesyl or 20-carbon geranylgeranyl groups to the C- termini of proteins in eukaryotic cells. We have shown that this post-translational modification occurs in Trypanosomatids and in malaria, parasites that cause devastating tropical diseases. We have also shown that the enzyme that attaches farnesyl groups to parasite proteins, protein famesyltransferase (PFI_), is a good target for the development of novel drugs that inhibit the growth of the parasite that causes African sleeping sickness (Trypanosoma brucei) and malaria (Plasmodiumfalciparum). We want to apply the principles of medicinal chemistry to improve the selectivity of PFF inhibitors for the parasite enzyme in preference to mammalian PFT. Our most promising PFT inhibitors will be tested on parasite-infected rodents. Gene disruption studies will be carried out to explore the requirement of PFr for survival of two other Trypanosomatids, Trypanosoma cruzi and Leishmania major. We will also study the biochemistry of two additional steps in the protein prenylation pathway, namely the proteolytic removal of the C-terminal 3 amino acids and the methylation of the famesylated cysteine residue. Parasite protease and methyltransferase will be cloned, expressed and kinetically characterized. Gene interference techniques will be used to explore the requirement of these enzymes for parasite viability. Our overall goal is to develop new drugs for the treatment of parasitic diseases that cause suffering among millions of people worldwide.